See Us On The Road at these upcoming tradeshows...
New Products
New High Channel Count Microwire Arrays
Tech Talk
You don’t have to wait for football season to do the wav…
Is your PC sleeping on the job?
Normalize speaker output with FIRs…
Why am I having problems using the BNC inputs on my RX6?
Dive in ...
Summer is here and that means fewer classes to teach or take. So what are you going to do with that extra time? Go to the beach, lake, or pool? No way! Time to dive into research. Our technical support team is fully staffed and ready to answer any questions that might come up when you set up that new experiment you’ve been putting off. You can learn more about our new recruits in our staff introductions. People aren’t the only new things you’ll find in this edition of the TDT Newsletter. Our product development team has been hard at work developing the new technologies you need. We're excited to share information about these new products, including new headstages, high channel count microwires, and a new headtraker interface just to name a few. As usual, you’ll also find a smattering of news, tips, and other great information. We hope you’ll take a few minutes and dive in!
Announcing ...
We are pleased to announce this year we'll be sponsoring The Tucker-Davis Symposium on Advances and Perspectives in Auditory Neurophysiology, a Satellite Symposium at the Society for Neuroscience Annual Meeting. The symposium will be held Friday, November 11, 2005 at the Washington Convention Center in Washington, D.C.
This one-day symposium, organized by Xiaoqin Wang, Ph.D. (Johns Hopkins University) and Yale E. Cohen, Ph.D. (Dartmouth College), will be held in conjunction with the annual Society for Neuroscience meeting to facilitate the growth of auditory neurophysiology research in awake and behaving mammalian models. This annual satellite symposium will provide an opportunity for researchers to meet on a regular basis, discuss issues unique to these studies, and share recent findings. The symposium will also make it possible for researchers working in other systems to learn about this exciting field. Find out more at: http://www.apan.jhu.edu/
New Products
Motion Tracker Interface
Features:
- Direct interface to Polhemus FASTRAK® or Ascension Flock of Birds® motion tracker
- X, Y, Z coordinates and roll, azimuth and elevation
- Input tracker data from two receivers/sensors
- 120 Hz update rate
- Digital signal to TDT RX or RP devices with a fiber optic input (such as RX5, RX6, or RA16)
The HTI3 is an interface between your System 3 processor and either the Polhemus FASTRAK® or Ascension Flock of Birds® motion tracker. The HTI3 allows researchers to seamlessly integrate movement and positional information into experiments running on the System 3 platform.
The HTI3 can input X, Y, Z coordinates as well as roll, azimuth and elevation data from two receivers/sensors. Data can be transferred directly to any System 3 processor with a fiber optic input, bypassing the host computer. This frees the computer for other tasks and ensures that motion and position information can be used in real-time without any increase in latency.
Using the HTI3 with the RX6 Multifunction Processor (with fiber optic port) you’ll be able to use tracker data to update a 3D audio signal presentation in real-time. Used with the RX5 Pentusa BioAmp System, the HTI3 simplifies the task of incorporating subject movement data into physiological studies of awake, behaving subjects.
Because the HTI3 also enables a direct interface with OpenEx projects, motion and position data can be stored systematically with other experiment data. The unique OpenEx data format supports fast and flexible data display and analysis, so you’ll be able to dynamically explore relationships between positional data and response data.
Contact TDT for more information.
Microwire Arrays - High channel count arrays, available now!
Looking for customizable electrode arrays that deliver reliable quality and performance?
TDT Microwire Arrays are simple and reliable electrodes for chronic multi-channel neurophysiology applications. With over 15 years of experience in manufacturing hardware for scientific applications, Tucker-Davis Technologies has the resources to reliably deliver the arrays you depend on for your research. Our manufacturing methods produce consistent, dependable, and affordable arrays while maintaining the flexibility to build custom arrays to your specifications. With TDT microwire arrays you can design your own electrodes without the time and labor intensive task of building arrays by hand.
Looking ahead ....
Our R&D department is continuing to expand our microwire offerings. Tetrode, stereotrode, and chisel tipped arrays are currently under development.
Chronic arrays eliminate the need for anesthetized and head-fixed preparations, and allow for recording and stimulation in awake, behaving animals in naturalistic settings. In addition to greater physical and behavioral freedom, chronic arrays provide long-term access to a block of neural tissue, and increase the data yield from each valuable experimental subject.
Microwire Array Configuration
All standard TDT microwire arrays use 50 µm polyimide-insulated tungsten microwire. This wire has excellent recording characteristics and its rigidity facilitates insertion. The standard array consists of 16-channels configured in two rows of eight electrodes each. Electrode separation is 250 µm within rows, with 500 µm separation between rows. The overall length of our standard array is about 2.5 cm, but can be customized simply by adjusting the length to which the microwire is cut. An optional epoxy “land” near the recording end of the array maintains electrode spacing.
Standard values are listed below. The user can request a custom value for most specifications.
n Rows X n Electrodes = [2X8] (Max channels per connector = 16)
Metal = [Tungsten] (Metal = Tungsten)
Electrode Diameter = [0.050 mm] (Electrode diameter of 0.050)
Insulation = [Polyimide] (Insulation = Polyimide or Formvar)
Row Pitch = [0.250 mm] (Row pitches of 0.250, 0.300, 0.450 mm + multiples)
Row Distance = [0.500 mm] (Row distances at 0.05 intervals from 0.05 - 0.8 mm)
Total Length = [25 mm] (Total length 15 - 120 mm)
Tip-to-Land = [2mm] (Tip-to-Land 2-4 mm)
Contact TDT for more information.
More New Products
32 Channel Headstage
The NN32AC 32-channel acute headstage has a 40-pin connector designed for use with the NeuroNexus Acute 32-channel probe. The headstage connects to two RA16PA preamplifiers via two 25-pin connectors. The NN32AC features the same low noise characteristics as our RA16AC 16-channel acute headstage with the same size footprint. Contact TDT for more information.
New Four-Channel Acute Headstages
The RA4AC1/RA4AC4 4-channel acute headstages have a low-profile 6-pin connector that can be used with standard high impedance (>1 MΩ) metal electrodes. The RA4AC1 provides unity gain (1x) and the RA4AC4 provides 4x gain. The 25-pin connector connects to the RA4PA 4-channel Medusa preamplifier. Contact TDT for more information.
Eight-Channel Power Amplifier
The SA8 is an eight-channel power amplifier that delivers up to 1.5 watts of power per speaker to up to eight speakers. The unit features high channel separation with low cross talk combined with low noise and distortion. The gain for all eight channels can be set to 0, -6, -10 or –13 dB using front panel toggle switches. Outputs are arranged for direct connection to a PP16 Patch Panel. Contact TDT for more information.
Multi-I/O Processor
The RX8 is the newest addition to our line of High Performance Processors. The RX8 targets those needing multiple channels of analog input or output. It offers up to 24 channels configured at the factory, offering users an opportunity to mix and match inputs and outputs as well as audio and PCM converters. With a sample rate at a screaming 100 kHz, providing a functional bandwidth of 40 kHz, the RX8 adds incredible versatility to the TDT System 3 line.
Depending on the configuration you choose, use the RX8 to:
- Drive speaker arrays.
- Acquire from microphone arrays.
- Drive cochlear implants.
- Control stepper motors.
Find out more about the RX8 on our Website.
New Faces at TDT
Customer Advocate
Michelle graduated from the College of the Holy Cross with a Liberal Arts Degree, spent some time in graduate school studying Anthropology and Museum Studies, and went on to work in research positions at the American Museum of Natural History and the Brooklyn Museum of Art. While she loves museums, she was working in a behind-the-scenes capacity and missed having regular interaction with people.
Michelle ventured into Project Management five years ago and found it very rewarding. She enjoyed working closely with her project teams and giving her clients personalized attention throughout the duration of their projects. Now that she has moved into the Customer Support position here at TDT, Michelle is every client's point of contact for upgrades, technical assistance and repairs. She looks forward to continuing to provide all her clients with prompt, friendly service and valuable information.
Applications Support Specialist
Andrew hails from Madison, Wisconsin. After earning a B.S. in Biomedical Engineering from his hometown institution, University of Wisconsin, he went on to study at University of Michigan. In pursuit of his M.S. in Biomedical Engineering he spent two years there working in a lab doing acute and chronic neural implants and recording.
Andrew comes to us already experienced with using TDT equipment for sound generation and neural recording and familiar with microelectrode arrays. His research lab experience makes him a welcome addition to the TDT Tech Support team.
Applications Support Specialist
Reema graduated with a Master’s in Biomedical Engineering from the University of Wisconsin-Madison. As a graduate student she worked in the MRI lab in the Department of Medical Physics. Her research included developing signal processing algorithms for breast cancer detection and shear stress estimation in carotid arties using MRI.
She received her Bachelor’s degree in Biomedical Engineering from the University of Mumbai, India. During her undergraduate education, she did an internship at a major hospital and medical research center in Mumbai, India where she did troubleshooting and maintenance of medical equipment. On the technical side, her interests have always been signal processing, instrumentation and product development.
On a more personal note, she enjoys cooking, biking, hiking, pottery and traveling and has completed a formal course in Indian classical dancing.
Documentation Engineer
Zak graduated from the University of Florida with a BS in Electrical Engineering with an emphasis in digital signal processing. He is currently finishing up requirements for his MSEE with a minor in Mechanical Engineering. His thesis project is a novel wavelet analysis software suite. This tool was developed for researchers at the Florida Museum of Natural History working with electric organ discharges of South American electric fish.
Tech Talk
You don’t have to wait for football season to do the wav…
Want to use a wav file as the stimulus for your next experiment? No problem. Most TDT software supports the use of wav files, but there are a few things you’ll need to keep in mind. First, wav files come in lots of varieties. We support 16-bit PCM mono files. Also remember that the TDT software will not resample the wav file. If you want the wav file to play out properly (and we’re betting you do) the sample rate in the wav file must match the sample rate used on the TDT hardware.
You can resample the wav file in Matlab or other audio editing software, such as Cool Edit. You can use wav files in SigGenRP when designing the component parameters of a signal segment. To use your wav with most other TDT software you’ll need to load the wav file to a buffer in RPvds.
If you are using lots of wav files, you might want to consider concatenating the wav files (with software such as Matlab) and then load the entire array of wav files to a single buffer instead of using a separate buffer for each wav. The RamBuf component allows the index parameter as an input, so after the wavs are concatenated into a single file and loaded to the buffer, you can select the correct wav file for playout by setting the index of the buffer to the appropriate offset.
The example code below reads in a .wav file and returns resampled data that is ready to play out on the DAC. The WriteTagV is used to load the data into the SerialBuf component of an RPvds circuit. In the example circuit, the data is fed to the SerialBuf using the "data_in" parameter tag.
Code it!
wav_filename = 'c:\tmp\myfile.wav' ;
% put path of .wav file here
new_sample_rate = 24414.0625 ;
% put sample rate of RPx here
[data, sample_rate, bps] = wavread(wav_filename) ;
[p, q] = rat(sample_rate/new_sample_rate, 0.0001) ;
new_data = resample (data, q, p) ;
invoke (RP, 'WriteTagV', 'data_in', 0, new_data') ;
invoke (RP, 'SoftTrg', 1) ;
This example can also be applied to other types of data (e.g. 16-bit integers).
Is your PC sleeping on the job?
Gigabit: I’ve got data for you.
PC: zzzzzzzzz…
Gigabit: No, really this data is important.
PC: zzzzzzz…
Gigabit: You know the researcher is going to blame me if we lose this data.
PC: zzzzzzzz…
Gigabit: What we have here is a failure to communicate.
PC: zzzzzzzz…
Gigabit: Arrg… I give up!
If you haven’t turned off your PC’s Hibernate and Standby features, this conversation could be happening in your lab. The Windows XP and 2000 Standby and Hibernate features automatically set your computer to a low power state or turn it off to conserve power during periods of inactivity. When your PC goes into one of these modes communication will be lost between your PC and your System 3 hardware.
You can turn these options off through your PC’s Control Panel. Open the Power Options dialog box and set Turn off hard disk, System standby, and System hibernates (only in view when hibernate support is enabled) to Never. Once that’s done, you’ll no longer have to worry about your PC sleeping on the job.
You’ll find more helpful news, anomalies, and tips in the System 3 Tech Notes section of our Website.
FAQ
Question: Why am I having problems using the BNC inputs on my RX6?
Answer: The BNC inputs IN-1 and IN-2 on the front panel of the RX6 are actually input channels 128 and 129 in RPvds. The channels are not the logical 1 and 2 because some versions of the RX6 also have fiber optic inputs that use the lower analog input channels.
Please see the Support page on the TDT Website for links to more FAQs on installation issues, OpenEx, RPvds, ActiveX, SigGenRP, and BioSigRP.
Using an FIR filter in an RPvds circuit to normalize speaker output.
SigCalRP is a great calibration program to normalize signals generated using SigGenRP, but what if your signals are being generated in your own RPvds file? This article explains how you can use SigCalRP and Matlab to generate FIR coefficients, then use them in RPvds to filter signals that will be played out to a speaker.
To generate your coefficients you'll follow these basic steps:
- Measure the transfer function (TF) of the system.
- Modify the calibration data in Microsoft Excel.
- Save the FIR coefficients to a text file.
The FIR coefficients generated in this example, can be used to filter signals of varying frequency and constant amplitude so that the sound output in units of dB SPL from the speaker will be constant over all frequencies. These coefficients will be generated for a circuit running at a specific sampling frequency. To work properly, they must be used in a circuit running at the same sampling frequency.
Measuring the TF of the system.
SigCalRP can be used to calculate the TF of a system for speaker calibration at sample rates up to 200 kHz. Before performing this operation, users should know the A/D and D/A conversion limitations of their specific hardware. For example, to perform a calibration at a 200 kHz sample rate, two RP devices must be used and an RP2.1 (200 kHz max A/D sample rate) must be used for signal acquisition. The figure below shows a typical setup using a single RP2 for calibrations up to 100 kHz.
Under Signal Setup in SigCalRP, enter the frequency step using the number of frequencies you wish to measure across the spectrum and the Nyquist frequency. For an RP2 running at 100 KHz and a filter of 200 points, the Nyquist frequency is 48828.125 Hz and the frequency start and frequency step are determined by the relationship:
48828.125/200 = 244.120625 Hz
Since SigCal cannot sample all the way up to the Nyquist frequency, run SigCal at 200 kHz to ensure that the Nyquist frequency of the device running the FIR (48828.125 Hz) is represented. Also, make sure that all test frequencies used are integer multiples of the Nyquist frequency of the device to avoid aliasing. Set the horizontal green bar in the calibration plot to the dB level you want to achieve for all frequencies using the filter. The filter will attenuate frequencies above the green bar and amplify frequencies below it. Use care when amplifying the signal. You will probably only want to amplify frequencies that will not be presented.
To export the data as a *.csv file, in the Calibrate menu select Export Calibration Data.
Modifying the calibration data in Microsoft Excel.
Open the *.csv file using Excel. The data can now be modified for use with Matlab’s fir2 function. The frequency argument of this function requires that the frequency be within the range 0.0 < F < 1.0, with 1.0 corresponding to half the sample rate (Nyquist frequency). To satisfy this requirement, insert a row before the first row of data in the table. In this row set frequency = 0 and Normalization (dB SPL) = the value of the first point (assume that this is not an important data range).
Copy the Normalization column into a Matlab vector named gain_list.
In Matlab type >> gain_list = [paste column from Excel]
Next, insert a column next to the frequency column. Set the values in this column equal to Frequency/Nyquist. At this time make sure that this column starts with a 0 and ends with a 1. Copy this column into a Matlab vector named freq_list.
In Matlab type >> freq_list = [paste column from Excel]
These two vectors can either be entered at the Matlab command prompt or at the beginning of the sample code that follows.
Saving the FIR coefficients to a text file.
This Matlab code segment will generate the FIR filter coefficients and save them to a text file named ‘C:\TDT\MyFIRcoefs.txt’. This text file can be used with a SourceFile component in RPvds to use the coefficients with an FIR filter.
ntaps = 250;
nyquist = 48828.125;
filtcoefs = fir2(ntaps,freq_list,10.^(gain_list/20));
fileid = fopen('C:\TDT\MyFIRcoefs.txt','wt+');
fprintf(fileid,'%6f\n',filtcoefs);
fclose(fileid);
This text file can be used with a SourceFile component in RPvds to use the coefficients with an FIR filter.
This Matlab code segment generates two plots. The first plot displays the calibration data used (blue line and circles) and the magnitude response of the generated FIR filter (red). The second plot shows the generated FIR filter coefficients.
subplot(2,1,1);
filtresp=fft(filtcoefs,1000);
plot(freq_list*nyquist,gain_list, 'b-o',linspace(0,nyquist,...
length(filtresp)/2),20*log10(abs(filtresp(1:length(filtresp)/2))),'r');
xlabel('Frequency (Hz)'); ylabel('Gain (dB)');
subplot(2,1,2)
plot(filtcoefs);
xlabel('Coefficient number'); ylabel('Coefficient value');
For assistance or more information about using FIR coefficients in RPvds contact our support team.
See Us On The Road at these upcoming tradeshows:BMES Neuroscience ARO |
Copyright 2006 Tucker-Davis Technologies, Inc. All Rights Reserved.